Impregnated nonwoven needled fabric consisting of a blend of synthetic fibers



NOV. 4, 1969 K, w, PAULlG ET AL IMPREGNATED NONWOVEN NEEDLED FABRICCONSISTING OF A BLEND OF SYNTHETIC FIBERS Filed NOV. l5. 1966 wwwa,

FIG l FIG 4 FIG 5 FIG 6` United States Patent O U.S. Cl. 161--148 6Claims ABSTRACT OF THE DISCLOSURE An impregnated nonwoven fabric isdisclosed, said fabric comprised of a needled batt which consists of ablend of stress-bearing synthetic fibers and nonstressbearinghydrophilic fibers, the binder being more heavily concentrated atdiscrete points corresponding to the ligations in the needled batt. Thestress-bearing fibers consist of 25-70% crimped fibers and 454.0%uncrimped fibers.

This invention relates to synthetic leather. More particularly, itrelates to an impregnated fibrous array suitable for use as a substrateto be finished into a leatherlike material for use in shoe uppers.

Leather substitutes generally are old in the art. Coated and impregnatedpapers have been used for many years, as have similarly treated wovenfabrics. Although satisfactory for certain static uses suc-h astable-top ornamentation, luggage, notebook covers and the like, paperhas insufficient, elongation to serve where the object must be molded ordrawn to irregular contours, as in shoe formation. Woven fabricsimpregnated with elastomeric polymers have found some limited utility inthe shoe trade, particularly as quarter linings, but lack ofextensibility and flex life has held such usage to low-priced shoes,where maximum service and comfort are not eX- pected. Prior art nonwovenfabrics, impregnated and coated, have also been the subject of intensiveexploration in the shoe upper field. Although they do have greaterelongation than paper or woven fabrics, in general conventionalimpregnated nonwoven fabrics have a relatively low tensile strength,tear strength, and flex life. By the use of special techniques andspecial binders, these deficiencies can be largely overcome, so thatcertain impregnated non-woven substrates can be produced which areacceptable so far as lasting processes are concerned, and which havegood strength, scuf resistance, and moisture vapor permeability. Inattaining such qualities, however, these recently developed substrateshave not achieved the one property which distinguishes real leather fromall nonleather prior art substrates of which we are aware: that is, theability to take a limited permanent set.

The fact that a limited number of sizes of leather shoes will serve withrelative comfort for a tremendous variety of shapes of individual feetis due in large part to the fact that leather, in addition to beingextensible, will after a few wearings shape itself permanently to thehighly individualized contour of the foot upon which it is worn. It isnot by happenstance that the phrase corn- "ice fortable as an old shoehas been long current, and it is generally recognized that leathershoes, in the breakingin period, adjust themselves to the contour of thefoot so that they feel comfortable, for broken in, even if worn onlyintermittently thereafter. This is because the interentangled fibers inreal leather, under stress, can slip past each otherAand becomerearranged along certain segments of their length, without becomingloosened from the main leather structure. It is characteristic of shoeupper leather that the fibrous structure will deform or rearrangereadily under stress, but only up to a certain point, which is usuallyat 10% or less elongation. This degree of elongation is notspontaneously recoverable: that is, the leather fibers do not act likean elastic member under moderate repeated stress, but instead they takeon a permanent set. If the leather is stressed beyond this point,inter-fiber slippage and fiber rupture occur.

Hitherto it has not been possible to our knowledge to reproduce thecharacteristic of permanent set in man made artificial leathers. Priorart non-'woven substrates for synthetic leather are in general of twotypes. Either they are relatively weak, and capable of excessivepermanent deformation, or else they have been fortified to the pointwhere they are extensible, but where there is no fiber flow under stressand no permanent deformation. Shoes made from the first class ofmaterial have so little recovery from stress that they rapidly becomeshapeless. Shoes made from the second class of material will conformduring wearing to a foot, due to elasticity, but assume no permanentdeformation, so that they feel like a new pair of shoes each time thatthey are worn. It is with improvements in the field of elongation versuspermanent set that the present invention is concerned.

It is a primary object of this invention to provide an impregnatednonwoven substrate suitable for converting to a leather-like material.

It is a further object of this invention to provide such a substratewhich matches Ythe elongation and the permanent set of real leather.

Other objects of the invention will appear more fully from the followingdescription and the drawings, in which:

FIGURE 1 is a schematic plan view enlarged of one embodiment of theinvention.

FIGURE 2 is a still further enlargement of a section of FIGURE 1.

FIGURE 3 is a schematic cross-sectional view of the material of FIGURE 2along the line A-A.

FIGURES 4, 5, and 6 are idealized sketches of the behavoir under stressof a pair of fibers in the product of this invention.

It has now been found that many of the properties of real leather,including permanent set, may be duplicated in a nonwoven fabric providedthat fibers of a specific type, arrayed in a specific geometry, arebonded with a range of polymeric bonding agents which are distributedthroughout the nonwoven fabric in a specific manner. The variousindividual elements of this invention, to the best of our knowledge,have never before been combined to bring out the unusual interplay ofelements which effects the present unexpected results.

The process of the present invention comprises the following steps:

(1) Assembling a fibrous batt comprising a blend of crimped anduncrimped fibers, preferably in isotropic distribution.

(2) Needling the thus-formed batt to provide spacedapart areas of highfiber density interspersed among areas of lower fiber density.

(3) Saturating the needled batt with an elastomeric polymer or blend ofsuch polymers.

(4) Hot-pressing the impregnated and dried fibrous batt so that thefibrous array is compacted and made more dense, approximating theapparent density of natural upper leather (around 0.8 gram per cubiccentimeter).

FIGURE 1 represents a needled and saturated batt of textile-lengthfibers, magnified about 10 times. FIGURE 2 is a further 10foldmagnification of a portion of FIG- URE 1, and FIGURE 3 is across-section along the line A-A of FIGURE 2. Referring particularly toFIG- URES 2 and 3, textile-length fibers, of a character specifiedbelow, are aggregated by a needling operation which forcibly reorients aportion of the fibers out of their normally horizontal planarorientation and carries them down and through the fibrous batt normal tothe principal plane of the batt. Such localized rearrangements aresometimes called ligations, in the sense that they are the end result ofa threadless stitching or sewing operation. In addition to thereorientation process, there is also a packing or aggregating effect, sothat the fibers are, in localized areas, brought much closer togetherthan they are throughout the main body of the fibrous batt. Local andspaced-apart areas f high capillarity are thereby established, so thatafter saturating such a batt with an aqueous polymeric binder dispersionand drying, the binder will be found to be concentrated to aconsiderable extent in irregularly-shaped core-like regions 4 of FIG-URES 2 and 3. In the areas between cores, the fibers 2 may carry somebinder substance in the form of a coating or encrustation, and there maybe scattered beads or nodes of binder substance 6 of FIGURES 2 and 3.But the fibers are for the most part free to move in the regions betweenthe high concentrations 4 of binder substance, while within said highconcentration areas they are essentially locked into place. Since thebinder in these high concentration areas extends in depth down throughthe batt as well as laterally on the surface, as shown in FIGURE 3,these areas will be referred to herein as plugs.

We have found that in order to duplicate the elongation vs. permanentset characteristics of leather, it is desirable that a fibrous blend ofboth crimped and uncrimped synthetic fibers be used. By crimped fibersis meant synthetic fibers which have been artificially crimped, usuallyby a mechanical process, into a wavy configuration typically havingbetween 8 and 20 peaks per inch, of such a nature that if the fiber isgently stretched to a straight configuration, it will be found to havebeen extended by between 10% and 33% of its original length.

In, addition, it has been found that tensile strength alone is not theprimary index of fiber choice if a close simulation of real leather isto be realized. When batts of different fibers, but of the same weight,were uniformly saturated with a polyvinyl butyral dispersion to the samedegree of add-on, the tensile strengths of one inch wide strips were:acrylic fibers 23, viscose rayon '28, polyester 35, polypropylene 50,nylon 52. Rather than use all nylon, however, we find that the moisturevapor transmission rate, strength, elongation, and permanent set ofleather are best matched by the use of a fibrous blend of the followingnature:

25%-70% crimped synthetic fibers 45 %-20% uncrimped synthetic fibers30%-10% hydrophilic fibers such as viscose rayon.

The synthetic fibers in the above composition are the principalstress-bearing members, as explained more fully below. Nylon is thefiber of choice, but for economic or other considerations the crimpedfiber fraction may be a blend of nylon with polypropylene fibers, whichare also crimped. The viscose rayon ribers, present preferably to theextent of not more than 30% of the fibrous array, are valuable inincreasing the moisture absorption, regain, and moisture vaportransmission of the product, and are not a substantial contributor tothe strength of the product. For best results the fibers should be inrandom or isotropic distribution, so that the strength of the product issubstantially equal in all directions. This may be accomplished bycross-lapping, air-lay techniques, or other means well known in thetextile art.

. The attainment of up to 10% permanent set in the products of thisinvention is not completely understood, but it appears to be a functionof the interaction between the binder, the crimped fibers, and theuncrimped fibers. One possible basis for explanation is shown in FIGURES4, 5 and 6, wherein 10, 10 represents a pair of localized highconcentrations of polymeric binding material, 12 represents an uncrimpedand 14 is a crimped textile length fiber, both 12 and 14 being bonded atthe points 10, 10. These figures are admittedly hypothecated andidealized, since there are many fibers, both crimped and uncrimped,which are bonded at two separated points along their length by anyadjacent pair of binder areas or plugs. Nevertheless, since there aresubstantial numbers of both crimped and uncrimped fibers in the product,there is a likelihood that for each uncrimped ber which follows astraight or cursive path between the points 10, 10, there is a crimpedfiber following a similar path.

If stress is applied to the material in a lateral direction, the initialeffect is shown in FIGURE 5, where the paths of the crimped anduncrimped fibers have to at least some extent become straighter. This isprobably the situation in many of the fibers on the outer surface of alasted shoe, with many of the uncrimped fibers in a generally straightconfiguration, and the crimped fibers in a similar configuration butcapable of further extension due to residual crimp.

If the surface of the shoe is then called upon to meet local stress, asfrom enlarged joints or other deformities of the active or passive foot,the product of this invention is capable of elongating further due tothe fact that the crimped fiber fraction between the binder areas 10, 10is capable of further elongation. In the absence of such local stress,the fibrous configuration in the shoe may be assumed to approximateFIGURE 5, where the uncrimped fiber segments 12 lying between binderplugs 10, 10 stabilize the structure.

In the presence of local stress, the crimp is assumed to be locallyremoved from the crimped fiber segment 141ying between the binder plugs10, 10, giving rise to the configurations shown in FIGURE 6. In thisprocess of fiber extension in the crimped fiber segments, there is acertain degree of slippage of the straight fiber segments 12 through thebinder plugs, or some plastic deformation of the binder plugs 10, 10, orboth. For this reason, the binder material must have certain properties,as set forth below.

The tensioned segments of the uncrimped fibers remain bonded, and offera degree of resistance to further deformation of the structure. As thecrimped fiber segments 14 are stressed, removing the crimp, theirresistance to further elongation, coupled with the residual resistance0ffered by the uncrimped liber segments 12, is sufiicient to overcome orwithstand the local stress. In order to match the unrecovered elongationor permanent set which is characteristic of natural leather, a level of10% unrecovered elongation is preferred in the products of thisinvention. The test method used to determine permanent set is explainedunder Example I, below.

EXAMPLE 1 A blend of the following fibers was formed into an isotropicbatt by cross-laying a garnett fleece of the following composition:

Percent 3 denier crimped polypropylene 40 3 denier nylon type 201,crimped 20 2.3 denier nylon type 420, uncrimped 20 3 denier viscoserayon, uncrimped 20 This batt was needled conventionally in a Hunterneedle loom at a density of 350 needlings per square inch. The needledbatt was then saturated with an aqueous emulsion containing thefollowing ingredients:

75 dry parts of a soft, film-forming acrylic resin (Hycar 2600 x 83,from B. F. Goodrich) dry parts of nitrile rubber (Hycar 1572 x 42) 10dry parts of semi-fluid acrylic resin (Daratack 74L,

Dewey and Almy) 5 dry parts of a zinc oxide dispersion, 60% solids 5 dryparts of a 60% clay dispersion 2 dry parts of a melamine resin 0.2 drypart of ammonium chloride catalyst.

The wet pickup Was adjusted so that about 150% solids by weight wasadded to the fibrous batt, so that after drying on dry cans theimpregnated product consisted of about 40% fibers and 60% polymericimpregnant.

In this form, the density of the product is about 0.4 gram per cubiccentimeter, and the material is too weak and soft to servesatisfactorily as a shoe upper material. The above product is thereforepressed in a platen press for 30 seconds at 150 p.s.i.g. with the topplaten at a temperature of 295 F. and the bottom platen at roomternperature. This pressure should be sufficient to increase the densityof the product to the preferred range of between 0.8 and 1.1 grams percubic centimeter, matching the density of natural leather. Thetemperature differential helps to give a smoother and more compactedorganization to the heated surface of the artificial leather, so that itcan respond properly to the conventional coatings and finishes which areapplied to the outer surface of shoe leather.

The properties of the above compressed artificial leather base werecompared with the properties of a good grade of shoe upper leather.

The air permeability and moisture vapor transmission of the artificialproduct were also equal or superior to the natural leather.

The permanent set of the product of Example I was compared with thepermanent set of the natural leather by cycling one-inch wide strips ofboth materials to an elongation of for seven cycles on the Instronmachine. After 24 hours standing after the last cycling, both theproduct of Example I and the natural leather showed an unrecovereddeformation, or permanent set, of 5%. A Widely known and used poromericsynthetic shoe material, in a comparable test, recovered its originaldimensions completely in less than 24 hours, indicating that it hadtaken no permanent set. As explained above, this property of conformingpermanently to local stresses is most important in shoe leather, and isan outstanding advantage of the product of this invention.

The particular types of fibers selected for use in the practice of thisinvention may be varied, provided that the preferred ratio of crimped touncrimped stress-bearing fibers set forth above is not widely departedfrom.

By stress-bearing fibers is meant those fibers, present usually to theextent of 70% or more of the total ber content, which largely determinethe physical properties of the fibrous part of the product. In general,at least 70% of the weight of the fibrous element will consist of fiberswhich have a tenacity of at least 3 grams per denier under standardconditions, and a wet tenacity which is at least of the dry tenacity.Nylon is a particularly valuable fiber for use in this invention, `sinceit enhances the tear strength of the product, which is reflected insewing or stitch-tear resistance needed to produce durable shoes. Thenylon, preferably present to the extent of at least 20% of the fibrouselement, may for economic or other reasons be blended with othersuitable stress-bearing synthetic fibers, such as the polypropylene ofExample I. It is desirable that the artificial leathers of thisinvention be not too soft and too readily deformable, nor should they betoo rubbery, bouncy, or resilient. Most of the commercially availablefilm-forming acrylic used as binders for nonwoven fabrics yield filmswhich are too soft, and are marked by low tensile strength, highelongation, and high creep. Nitrile latices in general yield films whichare too rubbery and elastic. Typical moduli of elongation were run onfilms cast from the acrylic latex, the nitrile latex, and the blend ofthe two lattices identified above in Example I.

Modulus in pounds per square inch at- We have found that a desirablerange of modulus for the binder used in this invention is from. l0 to 25pounds per square inch at elongation. One convenient, though notrestrictive method of arriving at such a modulus is to use as bindingagent a major portion (50% or more) of a soft, film-forming acrylicresin, a minor (10%-40%) of a rubbery elastomeric resin such as anitrile rubber, and a still smaller portion (2%-20%) of a semi-fluidcompatible polymeric plasticizer. Other binder combinations will suggestthemselves to those skilled in the art, the important considerationbeing that the binder should adhere well to the fibers and should have amodulus of between l0 and 25 pounds per square inch at 100% elongation.

Having thus described our invention, we claim: 1. An impregnatednonwoven fabric suitable as a base for artificial leather whichcomprises a needled batt of textile-length fibers consisting of a blendof stress-bearing synthetic :fibers which have a dry tenacity of atleast 3 grams per denier and a wet tenacity which is at least 75% of thedry tenacity,

said stress-bearing synthetic fibers comprising between 25% and 70%crimped synthetic fibers and between 45% and 20% uncrimped syntheticfibers,

the balance of said blend comprising between 30% and 10% ofnon-stress-bearing hydrophilic fibers,

said needled batt of textile-length fibers being bonded with a softpolymeric binding material,

said binding material being more heavily concentrated in a set ofdiscrete and spaced-apart points corresponding to the ligations in saidneedled batt than it is in the areas between said points,

said impregnated nonwoven fabric having a permanent set of not greaterthan 10%.

2. The product according to claim 1 in which the orientation of thetextile-length fibers is isotropic throughout the principal plane of thefabric.

3. The product according to claim 1 in which the uncrimped syntheticstress-bearing fibers are nylon and the crimped synthetic stress-bearingfibers are a blend of nylon and polypropylene.

4. The product according to claim 1 in which the References Citedtextile-length fibers comprise 25% to 70% of a blend of crimped nylonand crimped polypropylene; 45% to 20% FOREIGN PATFNTS of uncrimpednylon; and 30% to 10% of hydrophilic 9191500 2/1963 Great Bumm' ber.

5. The product according to claim 4 in which the 5 ROBERT F' BURNETTPrlmary Exammer hydrophilic fiber is viscose rayon. L. M. CARLIN,Assistant Examiner 6. The product according to claim 1 in which themodulus of the binder is between 10 pounds and 25 U.S. Cl. X.R.

pounds per square inch at 100% elongation. 10 161-154, 170

